It is desirable to assign elevator cars to service hall calls in a manner which maximizes the performance of the entire elevator system. This involves using a number of sophisticated algorithms which determine the number of passengers in the elevator cars, determine the traffic mode of the elevator system, estimate the number of hall passengers at each stop, and calculate the tradeoffs between different performance parameters. These algorithms can be implemented as a plurality of fixed rules.
However, difficulties occur at the boundary conditions for the fixed rules. For example, a rule which bases the system traffic mode determination partially on the time of day might be: "if it is between 7:00 AM and 9:00 AM and if &lt;other conditions&gt;, then set the system traffic mode to UP-PEAK". The difficulty with such a rule is that at 6:59 AM, all of the other conditions which cause the system traffic mode to be UP-PEAK may already be present, but because of the fixed rule, the system cannot be deemed to be in the UP-PEAK traffic mode. The operation of the system may change abruptly depending on the traffic mode, but the input conditions, the predominate traffic patterns, probably change gradually between 6:59 AM and 7:00 AM.
Similar problems exist for all of the other car assignment related algorithms. Generally, the input conditions change gradually and, for the most part, continuously while the response to those changes, i.e. the reactions of the system (and ultimately the assignment of an elevator car to a hall call), change abruptly and discontinuously as the inputs to the system transition through boundary conditions.